Abstract: A catalyst for reducing nitrogen oxides into nitrogen and water in the presence of a reducing agent, which comprises:(a) titanium;(b) at least one element selected from the group consisting of tungsten and molybdenum in a total amount of 10-25% by weight in terms of oxides; and(c) niobium in an amount of 0.1-2% by weight in terms of oxides.

Abstract: A catalyst for denitrizing nitrogen oxides contained in waste gases in the presence of arsenic compounds, which comprises: titanium and vanadium therein in weight ratios of oxides of titanium to oxides of vanadium ranging from 99.9:0.1 to 92.0:8.0, the vanadium being concentratedly contained in the surface layer of the catalyst up to 200 .mu.m in depth from the surface of the catalyst in concentrations of at least about 1.5 times as much as the concentrations of vanadium throughout the catalyst.The catalyst may further contain therein at least one of tungsten and zirconium.The catalyst preferably has micropores of about not less than about 50 .ANG. in amounts of 0.25-0.40 ml/g, and micropores of about 50-100 .ANG. in radius in amounts of about 10-40% by volume and micropores of about 1000-60000 .ANG. in radius in amounts of not less than about 10% by volume, respectively, based on the total volume of the micropores of not less than about 50.ANG. in radius.

Abstract: Here is provided an adsorbent for adsorbing and removing an arsenic compound which becomes a catalyst poison in a selective contact reduction process for removing nitrogen oxides (NOx) from a combustion exhaust gas by the use of an ammonia as a reducing agent and a denitrating catalyst.The adsorbent of the present invention comprises a material in which the total volume of pores is 0.2 to 0.7 cc/g and the volume of the pores having a pore diameter of 300 .ANG. or more is 10% or more with respect to the total pore volume, and the material is a specific element, its oxide, an ion-exchanged zeolite or the like.In addition, the present invention is directed to a method for removing the arsenic compound from the combustion exhaust gas by injecting the adsorbent into the flow of the gas on the upstream side of the denitrating catalyst.

Abstract: A catalyst for denitrizing nitrogen oxides contained in waste gases, which comprises:(a) titanium, and(b) at least one base metal selected from the group consisting of V, W, Mo, Mn, Cu, Fe, Cr, Co, Ni, Zn and Sn, the catalyst containing titanium and the base metals in amounts of at least about 50% by weight in terms of oxides based on the catalyst, and titanium in amounts of about 80-99% by weight in terms of oxides and the base metals in amounts of about 20-1% by weight in terms of oxides, respectively, based on the total weight in terms of oxides of titanium and the base metals, and the catalyst having micropores of about 50-75000 .ANG. in radius in amounts of about 0.25-0.45 ml/g, and micropores of about 50-100 .ANG. in radius in amounts of about 10-40% by volume and micropores of about 500-60000 .ANG. in radius in amounts of not less than about 10% by volume, respectively, based on the total volume of the micropores of about 50-75000 .ANG.

Abstract: A process for producing a composition which includes a perovskite compound, the process comprising:(a) subjecting a mixture of a hydroxide of at least one A group element selected from the group consisting of Mg, Ca, Sr, Ba, Pb and rare earth elements and a hydroxide of at least one B group element selected from the group consisting of Ti, Zr, Hf and Sn, to the hydrothermal reaction in an aqueous reaction medium;(b) adding an insolubilizing agent to the resultant reaction mixture to insolubilize water-soluble compounds of the unreacted A group element dissolved in the aqueous medium so as to adjust the ratio of the group A element to the group B element in a resulting composition to a desired A/B ratio; or(c) filtering, washing with water and drying the resultant reaction mixture to provide a solid reaction product, dispersing the reaction product in an aqueous medium to form a slurry, adding to the slurry a water-soluble compound of the A group element, and then adding to the slurry an insolubilizing agent t

Abstract: A process for preparing shaped catalysts or carriers mainly containing titanium oxide and improved in mechanical strength which comprises calcining a material mainly comprising titanium oxide or a substance convertible into titanium oxide on calcination in the presence of metatitanic acid sol or gel, said metatitanic acid sol being the one prepared by deflocculation of metatitanic acid obtained in the course of the production of titanium oxide according to a conventional sulfuric acid process and said metatitanic acid gel being the one prepared by adjusting said metatitanic acid sol to pH 1 or higher.